This invention relates to, in general, the cleaning of processing tubes, and more particularly, but not limited to, the removal of particles from a processing tube used for semiconductor processing.
In semiconductor wafer processing, the wafers are processed in a furnace which is in the shape of a cylindrical tube made of quartz. It is important that these be substantially free of any particles which can be deposited on semiconductor wafers which are processed therein. Particles deposited on the wafers can result in defects formed in the semiconductor device.
Therefore, in situ cleaning is performed periodically on the tube to try to remove loose particles present in the tube. After in situ cleaning, tests must then be performed on the tube to ensure that the number of particles present in the tube are below a minimum level. This test entails inserting dummy wafers which have a known quantity of particles thereon, running a temperature cycle, and then remeasuring the amount of particles on the wafer. If the particle count has gone up by a certain amount, the tube must then be cleaned, in situ, before a production run may start.
In the past, in situ cleaning involved using a vacuum wand having a triangular shaped head on one end (similar to a standard attachment for a vacuum cleaner used in the home). The vacuum pull was from the bottom of the head. The vacuum wand was inserted into the tube to vacuum any loose particles which had fallen to the bottom portion of the tube.
One of the problems with this method was that the vacuum head often scraped the sides of the tube which created more particles to be removed. These additional particles were created by scratching of the tube itself or by scraping of a film deposited on the tube. The scraping of the film caused the film to flake and create more particles.
In addition, the vacuum head focused the vacuum only in a lower quadrant of the tube, therefore, only loose particles which fell to the bottom or which could be dislodged by the vacuum were removed. Particles which were lodged in other quadrants of the tube were not removed by the vacuum. However, these particles could be dislodged during the processing of semiconductor wafers, resulting in defects formed on the semiconductor devices formed on the wafers. Basically, this crude method of removing particles was ineffective and needed much improvement.
If in situ cleaning fails to provide a certain level of cleanliness in the tube, it must be removed from a furnace bank and chemically cleaned. The process of removing the tube from the furnace bank is cumbersome and time consuming. The tube must first be cooled down from an operating temperature of approximately 400.degree. C. before removal. A new tube must be inserted and brought up to operating temperature. It would be desirable to have a more effective in situ clean in order to reduce the amount of times the tubes must be changed.